What Happens to Entropy in a Shrinking, High-Temperature Universe?

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Discussion Overview

The discussion revolves around the behavior of entropy in a contracting universe, particularly at high temperatures and small volumes. Participants explore theoretical implications, quantum mechanics, and the nature of entropy in both macroscopic and microscopic contexts.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that in a shrinking universe, while heat increases, the volume available for particles decreases, leading to questions about the behavior of entropy in such conditions.
  • Others argue that if entropy were to decrease in this scenario, it would imply that time's arrow points towards larger volumes and decreasing heat, suggesting that entropy still increases over time.
  • One participant questions whether entropy can decrease at the quantum level, noting that time may not exist at that scale, and references a low-entropy state at the universe's inception.
  • Another participant challenges the notion that time does not exist at the quantum level, emphasizing the necessity of space and time in formulating physics.
  • Some participants discuss the implications of loop quantum gravity and its attempts to reconcile gravitational interactions with quantum theory, while noting that this remains an unsolved problem.
  • There is a mention of local decreases in entropy, particularly in the context of crystal formation and biological processes, while acknowledging that overall entropy increases in isolated systems.
  • Questions are raised about the maximum amount of disorder and the driving forces behind increasing disorder in systems.

Areas of Agreement / Disagreement

Participants express multiple competing views on the behavior of entropy in a contracting universe, particularly regarding local versus global entropy changes and the implications of quantum mechanics. The discussion remains unresolved with no consensus reached.

Contextual Notes

Limitations include the dependence on definitions of entropy, the unresolved nature of quantum gravity theories, and the assumptions regarding local versus global entropy behavior.

KurtLudwig
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In a shrinking universe heat will increase, but also volume available to place particles will decrease. What happens to entropy when the volume gets very small and the temperature is very high?
 
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KurtLudwig said:
Summary:: Does entropy always increase even in a contracting universe?

In a shrinking universe heat will increase, but also volume available to place particles will decrease. What happens to entropy when the volume gets very small and the temperature is very high?
Dodging the question...

If you were to find that entropy is decreasing in this situation then you will find that time's arrow runs toward larger volumes and decreasing heat. So entropy still increases over time.
 
Thank you
 
Can entropy decrease on the quantum level? I have read that at the microscopic level there is no time, time only arises at the macrolevel.

I have read that our universe started with a very low entropy. Is it known why the entropy was low?
 
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Where have you read this nonsense? Time and space are the very starting point of any physics. There's no way to formulate physics without space and time, no matter whether you look at the fundamental "microscopic" laws (quantum theory) or the effective "classical" laws of macroscopic matter.
 
I did not write that space does not exist.

I have read in "Reality is not what it seems" a book by renowned physicist Carlo Rovelli that time does not exist at the quantum level. In the same book, it is stated that space is granular, that is, quanta of space. "Reality are covariant quantum fields. From the book, these fields do not live in space time, they live, so to speak, one on top of the other: fields on fields. Space and time that we perceive in large scale are our blurred and approximate image of one of these quantum fields: the gravitational field."

Personally, I like classical physics much better. I like calculus and Newton's, Gauss', Faraday's and Maxwell's Laws. All need space and time.
 
This is written from the point of view of "loop quantum gravity" I guess, and it's one attempt at the solution of the one big unsolved puzzle of physics, i.e., how to describe the gravitational interaction within the concept of quantum theory. It's unsolved though and thus, in my opinion, completely premature to write popular-science books about it.

The established theories of physics, including quantum theory and also relativistic quantum field theory (the standard model of elementary particle physics, describing all known matter and fields except gravity) work with a classical spacetime model (either Galilei-Newton spacetime for non-relativistic or Einstein-Minkowski spacetime for special-relativistic physics; or the description of these known constituents in a given classical general-relativistic spacetime for simple cases of such a spacetime like (anti-)deSitter spacetime).

Also unfortunately Nature doesn't ask which kind of physics we humans like more. She just behaves as she does, but the good thing is that all the math you use in classical physics also applies to quantum physics too!
 
KurtLudwig said:
Summary:: Does entropy always increase even in a contracting universe?

In a shrinking universe heat will increase, but also volume available to place particles will decrease. What happens to entropy when the volume gets very small and the temperature is very high?
I assume you know that entropy can decrease locally , as long as it increases over all in any isolated system. i mention this , because you bring up "entropy at the quantum level". what exactly are you asking?
 
On the microscopic level (quantum level), ions aggregate to form crystals. A crystal is more ordered than ions in a solution. Is that negative entropy?
Life itself, due to bio-chemical instructions from DNA, seems to me to be a process that reverses entropy on a local scale. I have read that overall, taking all life support processes into account, entropy (disorder or unknown information about a system) still increases.
I accept the judgement of physicists that overall entropy increases, but there seem to be short term local
exceptions.
Is there a maximum amount of disorder? What drives this increasing disorder?
 

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